Hannya is an ancient Sanskrit word that means wisdom and virtue. This yokai was once a human woman was consumed with rage, resentment and jealousy that transformed into a demonic Oni. It was said that strong emotions like jealousy can turn a person into a demon.
Popularly, Hannya masks are used in the Japanese Noh Theatre. Some people thought that the yokai Hannya is male, but it is actually a woman.